1. Field of the Invention
This invention lies in the field of video alphanumeric displays, which generally utilize computer generated signals which are impressed upon cathode ray tubes for display. A general requirement for the amplifiers to drive the cathode ray tubes is that they must be broad band and must have uniform gain from approximately 0 Hertz to 20-30 megahertz.
2. Description of the Prior Art
In the commonly used circuits which drive the cathode ray tube in such display circuits, inadequate attention has been placed upon the protection of the output stage of the power amplifier and instead, manual gain control of the input stage has been provided, so as to limit the overall gain of the system and in that way prevent overload of the output stage.
There are a number of serious disadvantages with this conventional type circuit. For example, it is expensive, because considerable manual labor time must be taken to adjust for proper operation the input gain control. Further, it has reduced reliability because it utilizes a variable potentiometer on the input which typically has lower reliability than fixed impedance elements. Also, it is non-automatic, and therefore, the setting must be changed for different signal levels and different operating conditions.